Melt container

ABSTRACT

An object of the invention is to provide a container for holding a melt of a metal and/or a melt of a metal salt, in which a melt container allows keeping a small amount of heat radiation of the melt, suppressing penetration of the melt and development of breakage or cracking to the minimum, holding the melt suitably, and also preventing the melt from impurity contamination. The melt container of the invention is a container for holding the melt of the metal and/or the melt of the metal salt, and has, sequentially from inside of the container, a first layer constituted of a refractory having an apparent porosity of 12% or less, a second layer constituted of a refractory having a thermal conductivity (at 800° C.) of 4 W/m·K or less, and a third layer constituted of a refractory having a higher thermal conductivity than thermal conductivity of the second layer.

TECHNICAL FIELD

The present invention relates to a melt container.

BACKGROUND ART

As a container for holding a melt such as a molten metal or a molten salt (hereinafter, described also as “melt container”), a heat-resistant metal container, an iron container in the form of a ladle or the like, and so forth are used. The iron container in the form of the ladle or the like ordinarily has a ceramic lining inside the container. As a material for the lining, an unshaped refractory such as a castable refractory is generally used.

In the iron container lined with such a refractory, if cracking or breakage is caused in a refractory layer while in use, the melt reaches an iron crust. Thus, the iron crust is damaged, and in a serious case, a problem of the melt leaching out occurs. In a case where the iron crust is damaged, peeling off the refractory layer and reconstruction of the unshaped refractory is needed. From an operational aspect, such a case decreases production efficiency and also causes a large economic loss.

So far, research and development have been conducted on various multilayer structures or refractory compositions in the melt container in order to prevent the melt container from damage or corrosion due to penetration of the melt.

Patent literature No. 1 discloses an induction furnace in which a multilayer lining structure is constructed by arranging a shaped material having a low permeability in an outer layer part of a lining material. The induction furnace is constructed with a two-layer structure in which the shaped material having the low permeability is arranged in the outer layer part of the lining material, and a dry unshaped refractory is arranged in an inner layer thereof in order to prevent a metal having a low melting point or a low boiling point, such as zinc, from penetrating into a texture in a lined refractory of the induction furnace.

Patent literature No. 2 discloses a rotary kiln constructed with a two-layer lining structure in which an impenetrable membrane is lined on an inner surface of an iron kiln body, and a brick layer is constituted inside thereof so as to prevent the iron kiln body from corrosion due to hydrochloric acid and zinc chloride contained in a raw material of activated carbon, a corrosive gas generated during manufacturing titanium oxide, or the like.

Patent literature No. 3 discloses a molten metal leakage detector for an induction melting furnace. In a case where an alloy containing a metal having a low boiling point, such as zinc, is melted in a molten metal-holding induction furnace for melting the metal, the induction melting furnace is constructed with a two-layer structure in which an inner surface brought in contact with the molten metal is constituted of a molten metal-holding lining formed by sintering a powdery refractory material, and a coil-holding lining constituted in a cylindrical shape with a castable cement is arranged in an outer circumference thereof.

Patent literature No. 4 discloses a refractory having a long service life for a non-ferrous metal, in which resistance to corrosion and spalling (a phenomenon of a refractory being peeled by a crack or breakage) is improved in a container for a blast furnace, a flash smelting furnace, a converter, a holding furnace and so forth for the non-ferrous metal excluding aluminum (copper, zinc, lead and so forth). The refractory contains Al₂O₃ as a main component, and further contains ZrO₂, Cr₂O₃ and SiO₂.

However, any research has not been conducted on a lining structure in consideration of densification, heat insulation and thermal conductivity of members that constitute the container in the melt containers described in the literatures, and the melt container has admitted of room for further improvement.

For example, use of a melt container having a higher performance is desired in a process for manufacturing high purity silicon by zinc reduction of silicon tetrachloride because incorporation of an impurity should be suppressed as much as possible. Specific examples of such a melt container include a melt container for holding a melt of zinc chloride by-produced in a zinc reduction reaction of silicon tetrachloride, or a mixed melt of the zinc chloride and zinc.

Zinc chloride by-produced in the process for manufacturing high purity silicon is ordinarily separated into zinc and chlorine by electrolysis of the molten salt, and separated zinc is recycled and reused as an agent for reducing silicon tetrachloride.

Because high purity silicon is used as a raw material for a semiconductor or a solar cell, incorporation of the impurity should be suppressed as much as possible in the process for manufacturing the high purity silicon. Therefore, in a case where by-produced zinc chloride is recycled and reused as described above, a container that allows preventing the melt from impurity contamination should be constructed as the melt container for holding the melt of by-produced zinc chloride or the mixed melt of the zinc chloride and zinc.

Until now, any melt container that allows suppressing penetration of the melt and development of breakage or cracking and further preventing the melt from impurity contamination has not been developed. In particular, any research has not been conducted on members for constituting the container for holding the melt of zinc chloride or the mixed melt of the zinc chloride and zinc as described above.

Therefore, development has been strongly required on such a melt container that allows suppressing penetration of the melt and development of breakage or cracking to the minimum, holding the melt suitably, and also preventing the melt from contamination.

CITATION LIST Patent Literature

Patent literature No. 1: JP H11-211359 A.

Patent literature No. 2: JP H6-26767 A.

Patent literature No. 3: JP H9-303971 A.

Patent literature No. 4: JP H7-61858 A.

SUMMARY OF INVENTION Technical Problem

A function required in a melt container includes three aspects described below.

(1) A heat insulating function for keeping a small amount of heat radiation of a melt.

(2) A holding function for keeping a small amount of penetration of the melt.

(3) A function for preventing the melt from impurity contamination from a holding container.

In a container for holding a melt of metal chloride such as zinc chloride, a flux effect on a metal or an oxide (a phenomenon of dissolving out the oxide and so forth present in a contact surface between the melt and the container) is generally large, and therefore the container has a problem in which the container is subjected to contamination due to dissolving-out of an impurity from a container material brought in contact with the melt. Therefore, the functions (1) and (2) described above should be obviously considered in the melt container. In particular, meeting a requirement of the function (3) described above is required in the container for holding the melt of metal chloride such as zinc chloride.

The invention has been made in view of the actual situation described above. An object of the invention is to provide a container for holding a melt of a metal and/or a melt of a metal salt, wherein a melt container allows keeping a small amount of heat radiation of the melt, suppressing penetration of the melt and development of breakage or cracking, holding the melt suitably, and also preventing the melt from impurity contamination.

Solution to Problem

The inventors of the invention have diligently continued to conduct research for solving the problem, as a result, have found that a melt container having a specific multilayer structure allows keeping a small amount of heat radiation of a melt, suppressing penetration of the melt and development of breakage or cracking to the minimum, holding the melt suitably, and also preventing the melt from impurity contamination, and thus have completed the invention based on the finding.

More specifically, the invention concerns items 1 to 5 described below, for example.

-   Item 1. A melt container, wherein the melt container is a container     for holding a melt of a metal and/or a melt of a metal salt, and     includes, sequentially from inside of the container, a first layer     constituted of a refractory having an apparent porosity of 12% or     less, a second layer constituted of a refractory having a thermal     conductivity (at 800° C.) of 4 W/m·K or less, and a third layer     constituted of a refractory having a higher thermal conductivity     than thermal conductivity of the second layer. -   Item 2. The melt container according to item 1, wherein when the     first layer is immersed and allowed to stand for 30 days in a melt     at 500° C., an amount of a material dissolved out into the melt for     the material that constitutes the first layer is 0.2% by mass or     less,

the refractory that constitutes the first layer has a thermal conductivity (at 800° C.) of 15 W/m·K or more,

the refractory that constitutes the second layer has an apparent porosity of 20% or less, and

the refractory that constitutes the third layer has an apparent porosity of 12% or less and a thermal conductivity (at 800° C.) of 15 W/m·K or more.

-   Item 3. The melt container according to item 1 or 2, wherein     temperature at an interface between the second layer and the third     layer when the melt at 500° C. is held for 30 days is lower than a     melting point of the melt. -   Item 4. The melt container according to any one of items 1 to 3,     wherein the melt container further has a metal layer outside the     third layer. -   Item 5. The melt container according to any one of items 1 to 4,     wherein the melt of the metal is a melt of zinc and the melt of the     metal salt is a melt of zinc chloride.

Advantageous Effects of Invention

A melt container of the invention allows keeping a small amount of heat radiation of a melt, suppressing penetration of the melt and development of breakage or cracking to the minimum, holding the melt suitably, and also preventing the melt from impurity contamination.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows one example of a schematic cross-sectional view of a melt container of the invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a melt container of the invention will be explained in detail.

Melt Container

The melt container of the invention is a container for holding a melt of a metal and/or a melt of a metal salt, wherein the melt container has a first layer constituted of a refractory having an apparent porosity of 12% or less, a second layer constituted of a refractory having a thermal conductivity (at 800° C.) of 4 W/m·K or less, and a third layer constituted of a refractory having a higher thermal conductivity than thermal conductivity of the second layer.

The melt container having such a constitution allows keeping a small amount of heat radiation of the melt, suppressing penetration of the melt and development of breakage or cracking, holding the melt suitably, and also preventing the melt from impurity contamination.

First Layer

The first layer brought in contact with the melt to be held is constituted of a densified refractory. Penetration of the melt can be suppressed by constituting the first layer of the densified refractory. The apparent porosity of the refractory that constitutes the first layer is 12% or less, further preferably, in the range of 5 to 10%. If the apparent porosity of the refractory that constitutes the first layer is within the range described above, the container tends to allow suppressing penetration of the melt.

Moreover, the thermal conductivity (at 800° C.) of the refractory that constitutes the first layer is preferably 15 W/m·K or more, further preferably, in the range of 15 to 20 W/m·K. If the thermal conductivity of the refractory that constitutes the first layer is within the range described above, thermal shock resistance of the melt container tends to be improved.

In the invention, the apparent porosity and the thermal conductivity are expressed by values obtained according to measuring methods shown in Examples described later.

Moreover, when the first layer is immersed and allowed to stand for one month in a melt at 500° C., an amount of a material dissolved out into the melt for the material that constitutes the first layer is preferably 0.2% by mass or less, further preferably, in the range of 0.05 to 0.2% by mass. If the amount of the material dissolved out into the melt for the material that constitutes the first layer is within the range described above, the melt can be prevented from impurity contamination.

Specific examples of the refractory that constitutes the first layer include a silicon carbide castable refractory. Constituents of the silicon carbide castable refractory are mainly SiC in the range of 75 to 90% by mass (preferably, in the range of 80 to 85% by mass), Al₂O₃ in the range of 5 to 15% by mass (preferably, in the range of 5 to 10% by mass) and SiO₂ in the range of 1 to 10% by mass (preferably, in the range of 3 to 8% by mass).

Second Layer

The second layer arranged outside the first layer is constituted of a heat-insulating refractory having a larger heat insulation performance than heat insulation performance of the first layer. The amount of heat radiation of the melt can be suppressed by constituting the second layer of the heat-insulating refractory having the larger heat insulation property than the heat insulation performance of the first layer. The thermal conductivity (at 800° C.) of the refractory that constitutes the second layer is 4 W/m·K or less, preferably, in the range of 1 to 4 W/m·K. If the thermal conductivity of the refractory that constitutes the second layer is within the range described above, the amount of heat radiation of the melt can be suppressed.

Moreover, apparent porosity of the refractory that constitutes the second layer is preferably 20% or less, further preferably, in the range of 10 to 20%. If the apparent porosity of the refractory that constitutes the second layer is within the range described above, the container tends to allow suppressing penetration of the melt.

Specific examples of the refractory that constitutes the second layer include a heat-insulating castable refractory. Constituents of the heat-insulating castable refractory are mainly SiC in the range of 0 to 40% by mass (preferably, in the range of 20 to 40% by mass), Al₂O₃ in the range of 30 to 70% by mass (preferably, in the range of 30 to 60% by mass) and SiO₂ in the range of 20 to 40% (preferably, in the range of 20 to 30% by mass).

Third Layer

The third layer arranged outside the second layer is constituted of a refractory having a larger thermal conductivity than thermal conductivity of the second layer. A melting line (a lower temperature region than a melting point of the melt) in a refractory layer can be prevented from displacing outwardly in the container by constituting the third layer of the refractory having the larger thermal conductivity than the thermal conductivity of the second layer. More specifically, leakage of the melt can be prevented by using, as the third layer, a highly heat-conductive refractory having the larger thermal conductivity than the thermal conductivity of the second layer because solidification of the melt is attained within the second layer. Therefore, even when a metal layer is constituted outside the third layer, a direct contact between the metal layer and the melt can be prevented, as a result, the melt can be prevented from contamination.

Moreover, breakage of the refractory due to a heat history (spalling) can be suppressed because a temperature gradient inside the highly heat-conductive refractory can be reduced.

Thermal conductivity (at 800° C.) of the refractory that constitutes the third layer is preferably 15 W/m·K or more, further preferably, in the range of 15 to 20 W/m·K. If the thermal conductivity of the refractory that constitutes the third layer is within the range described above, a temperature difference between inside and outside the third layer can be minimized to facilitate designing an inner surface temperature at a temperature equal to or lower than the melting point of the melt to be held.

Apparent porosity of the refractory that constitutes the third layer is preferably 12% or less, further preferably, in the range of 5 to 10%. If the apparent porosity of the refractory that constitutes the third layer is within the range described above, the container tends to allow suppressing penetration of the melt.

Specific examples of the refractory that constitutes the third layer include a silicon carbide castable refractory. Constituents of the silicon carbide castable refractory are mainly SiC in the range of 75 to 90% by mass (preferably, in the range of 80 to 85% by mass), Al₂O₃ in the range of 5 to 15% by mass (preferably, in the range of 5 to 10% by mass) and SiO₂ in the range of 1 to 10% by mass (preferably, in the range of 3 to 8% by mass).

The third layer is not particularly limited, if the third layer meets the characteristics described above, but is preferably constituted of the refractory identical with the refractory of the first layer.

The melt container of the invention may further have the metal layer outside the third layer. Strength of the melt container can be improved by having the metal layer. Specific examples of metal species for constituting such a metal layer include iron and stainless steel.

Specific examples of the melt of the metal include a melt of a metal such as zinc, aluminum and magnesium.

Specific examples of the melt of the metal salt include a melt of a metal salt such as zinc chloride, aluminum chloride and magnesium chloride.

Any kind of shape of the melt container is particularly applied, including a variety of shapes, such as a vertical cylindrical container, a horizontal cylindrical container, a box container and an inverted bell-shaped container.

The melt container in the shape of the cylindrical container can be obtained, for example, by constituting the first layer to the third layer inside a cylindrical metal container by making linings thereto and fully curing the linings.

The melt container of the invention preferably has a lower temperature at an interface between the second layer and the third layer when the melt at 500° C. is held for 30 days, as compared with the melting point of the melt.

In the melt container of the invention, the temperature at the interface between the second layer and the third layer when the melt at 500° C. is held for 30 days is controlled to be lower than the melting point of the melt. Thus, even if the melt is penetrated through the breakage or cracking of the first layer and the second layer, the melt solidifies at the interface between the second layer and the third layer, and penetration does not progress any more. As a result, the melt does not cause damage such as erosion when the melt reaches a metal crust in the outermost shell of the container.

Control of the temperature at the interface between the second layer and the third layer is attained by selecting a refractory material for the first layer and the third layer and optimizing thickness of the first layer and the third layer.

Moreover, the temperature at the interface between the second layer and the third layer is allowed to be lower than the melting point of the melt also by thickening the first layer and the second layer to some extent. In particular, the temperature at the interface between the second layer and the third layer is efficiently allowed to be lower than the melting point of the melt by thickening the second layer having a large insulation performance.

In consideration of economic efficiency for usage of each refractory, compactness of the container and so forth, the melt container is preferably designed so as to allow the temperature at the interface between the second layer and the third layer to be lower than the melting point of the melt while thickness of the refractory is suppressed to the minimum requirements.

Realistically, in consideration of the economic efficiency, the thickness of each layer is preferably allowed to be 200 mm or less, for example, when an outer diameter of the melt container is 40 cm or more.

Moreover, an outer surface temperature of the melt container when the melt at 500° C. is held for 30 days is preferably 200° C. or lower. If the outer surface temperature of the melt container when the melt at 500° C. is held for 30 days is within the range described above, the melt held in the melt container does not reach an outer wall, and thus a service life of the metal container is prolonged, and a heat energy loss can also be kept low.

The thickness of each layer is preferably designed so as to allow the outer surface temperature of the melt container when the melt at 500° C. melt is held for 30 days to be within the range described above.

Application

The melt container of the invention can be used for various applications. For example, in a method for manufacturing high purity silicon by zinc reduction of silicon tetrachloride, the melt container can be used for a condensing and liquefying device for condensing and liquefying a by-produced zinc chloride gas, or the by-produced zinc chloride gas and an unreacted zinc gas, a melt reservoir (receiver) for accumulating and reserving a melt of by-produced zinc chloride, or a mixed melt of the by-produced zinc chloride and zinc, a zinc evaporator attached to a reduction reaction furnace to supply a raw material zinc gas, and an electrolyzer for electrolyzing by-produced zinc chloride to recover zinc and chlorine.

In addition, the inventor of the invention has disclosed the condensing and liquefying device for recovering the by-produced zinc chloride and the unreacted zinc in the method for manufacturing high purity silicon by zinc reduction of silicon tetrachloride according to Japanese Patent Application No. 2009-168812 as already applied. However, a constituent material of the condensing and liquefying device is not particularly referred to.

EXAMPLES

In the following, the invention will be explained in more detail based on Examples. However, the invention is not limited to the Examples described below.

[Thermal Conductivity]

Measurement of thermal conductivity of a refractory was carried out by heating and holding a test specimen at 400° C. and 800° C., respectively, and in accordance with JIS R2616 “Testing method for thermal conductivity of insulating fire bricks according to a stationary heat flow method.”

[Apparent Porosity]

Measurement of apparent porosity of a refractory was carried out by heating and holding a test specimen at 1,000° C. in a reducing atmosphere, and in accordance with JIS R2205.

[Modulus of Rupture]

Measurement of modulus of rupture of a refractory was carried out by heating and holding a test specimen at 110° C. and 1,000° C., respectively, and in accordance with JIS 82213.

[Compressive Strength]

Measurement of compressive strength of a refractory was carried out by heating and holding a test specimen at 110° C. and 1,000° C., respectively, and in accordance with JIS R2553 “Testing method for crushing strength and modulus of rupture of castable refractories.”

Example 1 (1) Manufacture of a Melt Container

As members that constitute a melt container, refractory A (FLEXITE KERSIK-PB, made by NIHON TOKUSHU ROZAI Co., Ltd.) and refractory B (FLEXITE TM-65C3, made by NIHON TOKUSHU ROZAI Co., Ltd.) both having a composition and physical properties shown in Table 1, and a vertical cylindrical iron container (outer diameter: 75 cm, length: 75 cm, thickness: 6 mm) were used.

A lining of refractory A was made at a thickness of 50 mm inside the vertical cylindrical iron container to form a layer constituted of the refractory A (third layer). A lining of refractory B was further made at a thickness of 150 mm on the layer constituted of the refractory A (third layer) to form a layer constituted of the refractory B (second layer). Furthermore, a lining of refractory A was made at a thickness of 50 mm on the layer constituted of the refractory B (second layer) to form a layer constituted of the refractory A (first layer). Then, each of refractory A and refractory B was fully cured, and a melt container having, sequentially from inside of the container, the first layer to the third layer and a metal (iron) layer was manufactured.

(2) Evaluation of the Melt Container

Into the melt container manufactured in the section (1) described above, 80 kg of a melt of zinc chloride was introduced, an electric heater with protective tubing was inserted into the melt to control a temperature of the melt at 500° C., and the state was held for 30 days. An outer surface temperature of the melt container on the occasion after a steady state was 167° C.

Furthermore, the layer constituted of refractory A (first layer) was immersed and allowed to stand for 30 days in a melt at 500° C. Then, when an amount of refractory A dissolved out into the melt for the layer constituted of refractory A (first layer) was measured, the amount was 0.1% by mass.

Comparative Example 1 (1) Manufacture of a Melt Container

As members that constitute a melt container, refractory A having a composition and physical properties shown in Table 1, and a vertical cylindrical iron container (outer diameter: 75 cm, length: 75 cm, thickness: 6 mm) were used.

A lining of refractory A was made at a thickness of 200 mm inside the vertical cylindrical iron container to form a layer constituted of the refractory A (first layer). Then, the refractory A was fully cured, and a melt container (inner diameter: 35 cm) having the first layer and a metal (iron) layer from inside of the container was manufactured.

(2) Evaluation of the Melt Container

Into the melt container manufactured in the section (1) described above, 80 kg of a melt of zinc chloride was introduced, an electric heater with protective tubing was inserted into the melt to control a temperature of the melt at 500° C., and the state was held for 30 days. An outer surface temperature of the melt container on the occasion after a steady state was 359° C. The outer surface temperature exceeded a design target of 200° C.

Comparative Example 2

Thickness needed for allowing the outer surface temperature of the melt container to be about 150° C. was calculated for the layer constituted of refractory A (first layer) in Comparative Example 1 according to a heat transfer calculation. The result showed that the thickness of the layer constituted of refractory A (first layer) should be 1,500 mm in order to allow the outer surface temperature of the melt container to be 145° C.

A design of facilities for an effective container is quite difficult with 1, 500 mm in the thickness of the layer constituted of refractory A (first layer). Therefore, use of refractory A in a single layer was found to be unacceptable.

TABLE 1 Table 1 Refractory Refractory Item Unit A B Composition SiC % 82.5 29.1 (Main components Al₂O₃ by mass 8.7 43.6 only) SiO₂ 4.9 22.4 Thermal conductivity at 400° C. W/m · K 22 1.8 at 800° C. 18 1.9 Apparent porosity at 1,000° C. % 10 18 Modulus of rupture at 110° C. MPa 25.3 10.5 at 1,000° C. 57.9 16.7 Compressive strength at 110° C. MPa 179 48 at 1,000° C. >200 52

TABLE 2 Table 2 Comparative Comparative Unit Example 1 Example 1 Example 2 First layer: thickness mm 50 200 1,500 of refractory A Second layer: mm 150 — — thickness of refractory B Third layer: thickness mm 50 — — of refractory A Outer surface ° C. 167 359   145 temperature of melt container Amount of first layer % 0.1 — — dissolved out into melt by mass (after 1 month)

REFERENCE SIGNS LIST

1: Melt container

2: First layer

3: Second layer

4: Third layer

5: Metal layer

6: Melt 

1. A melt container, wherein the melt container is a container for holding a melt of a metal and/or a melt of a metal salt, and comprises, sequentially from inside of the container, a first layer constituted of a refractory having an apparent porosity of 12% or less, a second layer constituted of a refractory having a thermal conductivity (at 800° C.) of 4 W/m·K or less, and a third layer constituted of a refractory having a higher thermal conductivity than thermal conductivity of the second layer.
 2. The melt container according to claim 1, wherein when the first layer is immersed and allowed to stand for 30 days in a melt at 500° C., an amount of a material dissolved out into a melt for the material that constitutes the first layer is 0.2% by mass or less, the refractory that constitutes the first layer has a thermal conductivity (at 800° C.) of 15 W/m·K or more, the refractory that constitutes the second layer has an apparent porosity of 20% or less, and the refractory that constitutes the third layer has an apparent porosity of 12% or less and a thermal conductivity (at 800° C.) of 15 W/m·K or more.
 3. The melt container according to claim 1, wherein temperature at an interface between the second layer and the third layer when the melt at 500° C. is held for 30 days is lower than a melting point of the melt.
 4. The melt container according to claim 1, wherein the melt container further has a metal layer outside the third layer.
 5. The melt container according to claim 1, wherein the melt of the metal is a melt of zinc and the melt of the metal salt is a melt of zinc chloride. 